Logarithmic amplifiers have been widely used in various equipment and instruments including spectrum analyzers, communication equipment, etc. to provide a wider dynamic range. For example, input signals having a dynamic range of over 70 dB may be amplified.
One conventional approach to logarithmic amplifiers is the use of several cascaded logarithmic amplifier stages, in which each stage becomes a unity gain amplifier sequentially from the output stage as the input signal level increases. Such logarithmic amplifiers are disclosed in U.S. Pat. No. 3,646,456 to Kauffman et al. and Japanese Patent Publications Nos. 35270/77 and 4055/81 all assigned to the assignee hereof. A disadvantage of such logarithmic amplifiers is the high component count, with the attendant high cost, long assembly time and danger of reduced reliability.